Air swept tube mill with pocketed liner structure for automatic classification of grinding bodies and ground material



Dec. 8, 1953 J A. SLEGTEN 2,661,908

- AIR SWBPTTUBE MILL WITH POCKETED LINER STRUCTURE FOR A'B'FGHATIC CLASSIFICATION OF GRINDING BODIES AND GROUND MATERIAL Filed May 8, 1950 a Sheets-Sheet 1 IN V EN TOR.

HTTORNEVS.

Dec. 8. 1953 J. A. SLEGTEN 2,661,908

AIR SWEPT TUBE MILL WITH FOCKETED LINER STRUCTURE FOR AUTOMATIC CLASSIFICATION OF GRINDING BODIES AND GROUND MATERIAL 3 Sheets-Sheet 2 Filed May 8, 1950 R Q W m4 m a 5 m gm r y m L Y Q 1 I I I 7 V... a a a B Dec. 8, 1953 2,661,908

- J. A. SLEGTEN AIR .SWEPT TUBE MILL WITH POCKETED LINER STRUCTURE FOR AUTOMATIC CLASSIFICATION 'OF GRINDING BODIES AND GROUND MATERIAL I Filed May 8, 1950 5 Sheets-Sheet 5 IN V EN TOR.

IWTORNEY-S.

Patented Dec. 8, 1953 UNITED STATES 2 661, .AIR SWEPT TUBE MILL WITH POCKETED LINER." "STRUCTURE non 'AUIQM ZHC CLASSIFICATION" OF GRINDING opms AND GRO ND MA IAL- Y Jean A. Slegteh, Brussels; Belgium Application my 1.8, 1950, sera1;o; g,v

T i nv n n rel s o t e mm ut eh 9 materials occurring in a substantial range of par;- ticle size and is concerned more particularly with tra hin n nd n wh e meteitihl t .be reduced to the desired state of fineness is subjected to classifying as an incident togrinding. The method may be practiced most advantageously in a mill of the tube type, which includes a cylindrical chamber rotating on a substantially horizontal axis and provided at one end with ain inlet for material to be treated and, at the other, with means for discharging the finished material. A mill forpraoticing the method is of'novel construction and the invention includes the new mill.

Heretofore, various methods of crushing or grinding material of the type described have been employed, such as thatemployed in a conical ball niill wherein automatic classification according .to particle size is produced by the conical slope of the entire mill drum and the rotation thereof. .In this type of gri ding or crushing, the coarse material lies toward or adjacent the inlet of the mill, because of the slope of the mill walls, and the particles of material diminishin size toward the apexof the conical portion. .TIfhe material being ground is classified becauseof the sliding rotating movement of the particles within the conical drum, the heavier particles 1novi ng toward the base ofthe cone byagitation and the .force of gravity. The problem-of removingthe fines as soon as possible after they are forn' edis at e fi u heeehs t ar m ed Wi hi coa e rf aet jthr us ou he i din hone and ub tore q al e vt t ey arivehea th ape Qft ew Ifa ehrhehte air is passed through the interiorof thernill-f or the urp see remwihs t ma e ia in its fi sh ds n e at ev y law h ce teg h the hue w l he i kedh b th eu en rn a th .bas e of the cone, ,but the air will pick lip-the argest p h e t ee the fi e a th rd haree em or ap x of h -.mi ,;w er the eeu atiqn is, greatest. V e

.fI i accqrdin lylg mqne the urno e ef hi invent on to..;p.r, vid 7 mi ha :Wi eutqmet .-.ea y ela s y the ihd bod es -b h ehe h const c i f th gmi 'l; i r ds else ef ect automa ic a sificatio o h mater h th e Q b twee -,th m l e ocket an a current of air passing through the mill.

@I ne :th a para us o "t inv nt c m rise a en rally ri onta ly disposed eloh atedrey ndr ea ha e "ha n anrz n et atlonelehd .for.: he...materia1, to be ound. and

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2 an outlet at the other-"end, through which the ground material cfan'be' discharged. "The mill cylinder is divided into two'ma in chambers} the first of which is a crushing chamber-at the inlet end of thernill; 'lflie other chamber of the mill is a grinding chamber," or attrition milLand-it is provided with line! sections of' frusto-conical shape abutting each {other to form the grinding surface 'Yand'ialso' to provide a nieans for automatically c1assijfying"the grinding media. l he surface of .ac'h'lsection exposedto the material being .groundis 'providedwith a series of openings .witha .poclietj beneatheach opening. A current of airis passed" throughthe millfor the purpose of classifying the material being ground and for the'fiirther purpose 'of'Idi scharging-part of the material of a desired fineness through the material outlet." Themateria' fienters through the inlet opening into thecrushingchamber of ,the mil l, where mixed media operate the crushing. As the"mate1jial flows into ;the*grind-i-ng chamber f the min containing the momma frusto-conical liner 1 sections; the final domr'niriution begins. "jBec'aujseof" the sloping s urfaces of the liners,.thegrindingliodies'will automatically be classified with the jlarg'erjbodies locat'ed in the initial grinding Zbl:1 (5 f 'th;e grinding chamber and the re alnd r of "ltheibodies' progressively decreasing fin sizeQt ward the discharge end the with the smallest bodjes lying'adacent the ma terial outlet. Similarly, fthebo'mbined action of .the liner pockets ahd{air stream" will classify the material being injd according-to particle size with the larger particles the initiahgrinding zone of the"; ll'and thejparticles i g-ressiviy decreasing in 7 ize' toward the-diScliarge end.

As the material' beingfground i'n' any" part r the r ndingfhamlirj'fine's willibe'pr'oduced as a result of t e 'riacturmg of the larger ipaiticles of-materialT Thseffihes wlill .enterinjto ,those pockets of the ihd'iyidual liner sections," which lie beneath the ;,nia'tei'iall '.Asthe"'rotation con} t me the fille hfoeke s he' upper part ofthe mill wherithe "renal contained mine pockets is dischargedfromlthe ipioc' hemete ihe s'es' a ,flowingthrougEthe grindmg chamber? f During {their iitajth particles undergo .a gravimetric separation, the larger fa11"with"a higher ,speedand rnor e or lessvertically while thetiniest lare deflected by the-mill sweep glair and entrained in d re :t",on .of Zthe outlet before they drep gntheg ind ,gmeiija; j'energtiic n e th elesa es eh efthe meh material to progressing quicker towards the smaller grinding media where they are ground more eificiently and so on until they reach the mill end, in the flow of material or entrained to the dust collector. The larger particles fall practically vertically and. remain under the action of the bigger steel media, until their specific surface is sufiiciently in creased to make them sensible to the axial air current, pulling them forward in such the greater steps as they are tinier.

By controlling the quantity or speed of cooling air, the progression of-the fine particles can be changed and at the same time the average size and the fineness of the final ground product.

From the use of liners according to the invention, results an important saving in power absorbed per barrel of ground material. The temperature rise is lower and also steel wear and maintenance. Grinding efficiency increases for two causes; the permanent elimination of fines cushioning the attritive action and the continuous assorting of medium and particle sizes for top grinding efiiciency. It has been proven that the relation between sizes of particles and media affects the efficiency in such range as from 1 to 5, keeping within conditions common in the industrial grinding practice.

In order that my invention may be clearly understood, it will be described with reference to the accompanying drawings, in which:

Fig. l is a vertical diagrammatic view, partly in section and with parts omitted, of a preferred form of apparatus for the practice of the new method;

Fig. 2 is a longitudinal cross-section through the center line of the mill;

Fig. 3 is a partial cross-section of the mill showing the classifying chambers of the tube mill;

Fig. 4 is a View similar to Fig. 3 showing a modified form of the liner chambers;

. Fig. 5 is a longitudinal cross-sectional view of the tube mill liners on an enlarged scale.

Referring to Fig. 1, a bin or hopper l controlled by a suitable valve 2 contains the raw be ground. A material conveying tube 3 is connected at one end to the feeder and, at the other end, to an air admission valve 4 .positioned between the material discharge tube 3 and the tube mill material inlet 5. The tube mill 6 is provided at its ends with hollow trunnions 1, 8, supported in bearings 9, l0, respectively, the passage through trunnion 1 forming the material inlet 5 and the passage H through trunnion 8 forming the material outlet.

The tube mill is divided into two main chambers l2, l3 and the initial crushing of the raw "material takes place in chamber 12. The second main chamber I3 is the grinding chamber and it is provided with a grinding surface comprised of individual frusto-conical sections 19, each section abutting the adjacent section to produce a series ofindividual frusto-conical zones throughout the grinding chamber iii. A grid g separates the crushing chamber from the grinding chamber and'maintains the crushing elements in the crushing chamber at all times, while permitting the raw material after a desired crushing action to be passed into the grinding chamber.

Each liner section I9 is made up of individual elements 20 which, as shown in Fig. 3, are of shell construction so that there is a pocket 2! having an opening 22 between adjacent elements around the inner periphery of the tube mill.

A fan 23 is provided to produce a current of air fiowmg through the mill 6 for the purpose of cooling the mill, and to classify and entrain, according to their individual size, the particles dropping from the pockets. The fan is equipped with a suction line 24 connected to the outlet sieve 25, which receives the material discharged from the tube mill through outlet II and has a discharge spout 26, through which material removed from the air is discharged into a reoe1 ver 21 whence it is conveyed to any desired point for further processing. As the air leaves the sieve 25 through the suction line 24, some of the finely ground material is still entrained in the air stream and the air and material are passed through a dust collector 23, wherein the material is completely removed from the air. ThlS material is conveyed from separator 28 through a discharge spout 29 to discharge spout 26, and the exhaust air from the separator 28 is vented through a vent stack 30 to the atmosphere.

The mill 6 is rotated by any convenient means,

such as a gear 35 attached to the mill casing and driven through a geared shaft 365 by any convenient conventional prime mover, not shown. In the operation of the apparatus, the fan 23 is started as soon as the mill starts to rotate, and it maintains a current of air through the mill system. The air enters the mill system through the air admission and the material inlet ll, flows through the two chambers l2 and I3, issues from the mill through the material outlet ll, passes through the sieve 25 and the dust collector 23, and exhausts from the mill system through the vent stack 38.

The material from hopper I passes throu h the discharge tube 3 and enters the mill throu h the material inlet 5. As the material enters the chamber I2, the crushing takes place. The mater al is progressively reduced in size by the m xed grinding bodies, after which it enters the gr nding chamber 13 for the final phase of commmution.

The grinding bodies in the grinding chamber l3 are automatically, classified by the inherent classifying action of the frusto-conical liner sect ons, with the largest of the grinding bodies 1"- ing ad acent to the inlet of the grinding chamber and the bodies gradually decreasing in size so that the smallest bodies lie adjacent the ma terial outlet of the mill.

An automatic classification accordin hole size of the material to be ground, gi ;duced by the combined action of the pockets 2| of the liner sections and the current of air flowmg; through the grinding chamber.

n eac zone of the grindin cha material is produced by the bre aking i fp of larger particles and the finest particles are re moved from the zone, in which they were produced, as soon after they are formed as posslble. This result is achieved as follows. As the particular pocket is rotating beneath the material charge in the mill, the ground mat rial enters and fills the pocket. When the pocket s elevated to the upper section of the mill the mater al in the pocket flows out of the pocket opening and falls toward the bottom of the mill through the current of air flowing h l'nllL- The material, that has been go n d t a sufi'icient fineness, is entrained in the air stream and carried towards the mill end with the air, and the heavier particles falling faster remain behind in the grinding zone in presence of relatively big grinding bodies more appropriate for further grinding of heavier particles.

The ground material passes through the outlet ll into the sieve 25 and further into the receiver 2! whence it is conveyed elsewhere for further processing. The current of air leaving the sieve 25 through the tube 24 carries with it a certain amount of fine material, which is separated from the air in the dust collector 28 and discharged through tube 29, while the air passes out through the vent stack 30.

A modified form of liner section is shown in Fig. 4, the section being made up of individual elements 34 spaced to provide pockets 33 having openings 3| of substantially the same width as the pockets. Within each pocket can be mounted a screen 32 overlying the pocket opening and provided with openings of the desired size to restrict the size of ground material which may enter the pockets and thereby avoid possible clogging of the openings by particles of larger sizes.

I claim:

A mill for crushing and grinding material, which comprises an elongated cylindrical member containing a crushing chamber and a grinding chamber adjacent each other and arranged for free flow of material from the crushing chamber into the grinding chamber, an inlet for admission of material into the crushing chamber, an outlet for material from the grinding chamber, means for rotating the cylindrical member, a series of frusto-conical liners in the grinding chamber, grinding bodies on the liners, the grinding bodies on the successive liners diminishing in size progressively toward the material outlet, means for causing a current of air to enter the crushing chamber through the inlet, flow through the two chambers, and exhaust through the outlet, and a plurality of pockets in each liner each having an opening through which ground material may enter the pocket, when the pocket is at the bottom of the grinding chamber, and may be discharged therefrom when the pocket is at an upper portion of the grinding chamber, the material discharged from each pocket entering the air stream, screening means extending across the openings into said pockets to restrict the size of ground material which may enter the pockets, whereby some sufficiently ground material is carried out of the chamber and insufficiently ground particles are advanced and are deposited on the JEAN A. SLEGTEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 689,347 Hundeshagen Dec. 17, 1901 953,092 Kennedy Mar. 29, 1910 1,369,061 Tetley Feb. 22, 1921 1,118,775 Hyde Nov. 24, 1924 1,541,114 Carman June 9, 1925 1,591,941 Newhouse 1 July 6, 1926 1,692,974 Barker Nov. 27, 1928 1,780,132 Jaedel Oct. 28, 1930 1,788,825 Danks Jan. 13, 1931 2,042,254 Godinez May 26, 1936 FOREIGN PATENTS Number Country Date 2,385 Great Britain of 1902 

